This invention relates in general to contact lens disinfecting apparatus and more particularly to a compact contact lens disinfecting and storage unit suitable for portable use.
The necessity for periodically disinfecting contact lenses and particularly soft contact lenses is well known. A variety of disinfectors is known in the art, including those shown in U.S. Pats. Nos. 3,998,590, 4,379,965, 4,472,623, 4,529,868 and 4,578,566, as well as other patents noted therein. Additional disinfectors are shown in French Patent Nos. 2,369,847 and 2,451,195.
Prior art disinfecting units are operated more slowly than is sometimes desirable. This is true as to those units that have heated the lenses within a separate carrying or storage case. Such an arrangement impedes the transfer of heat from the disinfector to the lenses. The one-piece disinfecting units have also disinfected more slowly than is desirable but for different reasons that will be discussed in detail infra. Lenses are ordinarily disinfected at night while the wearer sleeps and the length of the disinfecting cycle is of little importance. However, when disinfecting is forgotten and must be done in the morning, it is an advantage to be able to disinfect the lenses quickly. For example, the diffference between a 45 minute disinfecting cycle and a 20 minute cycle is the difference between being able to complete the disinfecting cycle while showering or bathing and having to wait for the cycle to be concluded. A disinfecting unit capable of a short cycle time is very desirable.
Prior art disinfecting units have also been undesirably expensive. The manufacturing cost of a disinfecting unit is directly related to the number of parts comprising the unit the need for high precision parts and the difficulty of assembly. The reliability of a unit generally increases when the number of parts is reduced. There is a need for a reliable, low-cost short cycle time disinfecting unit.
The art has recognized that at minimum, a disinfector must include a lens holder, a heating device, a power source and either a thermostat time control, or manual means for disconnecting the heating device from the power source. Positive temperature coefficient (PTC) heaters have been advantageously employed as heaters. PTC heaters have the advantages of low cost, ease of use and high reliability. In order to most efficiently use a PTC heater as a heat source, it is desirable to interpose a heat sink between the heater and the chamber in which the lenses are placed. The heat sink reduces the rate at which the temperature of the PTC heater changes and reduces the likelihood that the PTC heater will develop hot spots that could damage the lenses. Heat sinks distribute heat to the chamber uniformly and allow more heat to be transferred from the PTC heater to the chamber in a given time than is possible by using a PTC heater alone. This is due in part to the characteristics of PTC heaters. Such heaters have a slight negative coefficient of resistance vs temperature below the transition temperature of the device. Above the transition temperature the resistance increases rapidly with increasing temperature. As the resistance of the device increases, the current flowing through the device decreases and the power consumption is reduced. By thermally coupling the PTC heater to a heat sink rather than directly to a lower thermal mass lens-holding well, the temperature increases more slowly and more power is converted to heat for increasing the temperature within the well. Even after the PTC heater transition temperature is reached and the heat output of the PTC heater is substantially reduced, the heat sink continues to transfer heat to the lens-holding chambers, maintaining the temperature within the chambers at a sufficient level to continue the disinfecting process.
A variety of types of heat sinks may be used. One known disinfecting unit includes a substantial volume of waxy material surrounding the PTC's and the lens-holding chambers. The heat necessary to convert the wax from a solid to a liquid is extracted from the PTC's during the heat up phase and is thereafter transferred from the wax to the lens-holding chambers even after power is removed from the PTC's. While this construction provides a disinfecting function, it is inefficient and slow. Much of the heat stored in the melted wax is wasted by radiation through the case rather than heating the lens-holding chambers. The time required to heat and cool the wax is longer than desirable.